A surface of a metal substrate has hitherto been subjected to lamination processing so as to protect the surface of the metal substrate and to apply a design. A laminated film to be laminated on the surface of the metal substrate is excellent in processability, corrosion resistance, barrier properties of contents, and the like. Unlike a coating material, the laminated film is free from volatilization of an organic solvent, or the like, in the step of applying to the metal substrate, and is preferred in view of production environment. Therefore, the laminated film is widely used as protective materials of the surfaces of the metal substrates for packaging to be precoated in the form of a coil or a sheet, such as food cans, designed cans, capacitor cases, and battery members.
The laminated film has the above-mentioned excellent properties. However, in a material in which a surface of a metal substrate is subjected to lamination processing, a laminated film was sometimes peeled from the metal substrate, because of insufficient adhesion between the metal substrate and the laminated film, in the case of subjecting the laminated material to high-level processing as a packaging material, or in the case of adding contents to the packaging material after processing, and then subjecting to a heat treatment. Peeling of the laminated film from the metal substrate impaired aesthetic appearance of the laminated material to mainly cause deterioration of corrosion resistance of the laminated material.
To solve these problems in the laminated material, Patent Document 1 discloses technology in which a surface treatment layer is formed on a surface of a metal substrate using metal surface treatment composition prior to lamination processing to improve adhesion between the laminated film and the metal substrate. Patent Document 2 discloses, as a metal surface treatment composition used in a surface treatment with a surface treatment agent of an aluminum-based metal substrate, a metal surface treatment composition which contains a basic zirconium compound and/or a cerium compound, a carboxyl group-containing resin and an oxazoline group-containing acrylic resin, and is free from fluorine, and the document also discloses that it is possible to apply a metal material, in which an aluminum metal substrate treated with such metal surface treatment composition is subjected to lamination processing, for a battery outer casing.
Patent Documents 3 and 4 disclose that a material, in which a laminated film is bonded to a surface of a metal substrate, is used as a battery member for a lithium ion battery. As mentioned above, when using, as the battery member, the material in which a laminated film is bonded to a surface of a metal substrate, remarkably high adhesion between the laminated film and the metal substrate is required since it is necessary to sufficiently endure use over a long period. When using the above-mentioned material as the battery member, excellent corrosion resistance (particularly, hydrofluoric acid resistance and alkali resistance) are also required since the material is continuously exposed to an electrolytic solution.
[Patent Document 1] Japanese Unexamined Patent Application, Publication No. 2008-183523
[Patent Document 2] Japanese Unexamined Patent Application, Publication No. 2009-84516
[Patent Document 3] Japanese Unexamined Patent Application, Publication No. 2011-76735
[Patent Document 4] Japanese Unexamined Patent Application, Publication No. 2011-187386